1. Field of the Invention
The invention is concerned with a hydrostatic control system for a ground driven vehicle, which hydrostatic control system comprises a pair of hydrostatic pumps each controlled by a servo valve and a pair of hydrostatic motors each driven by a respective one of the pumps. Each of the motors drives ground engaging means such as endless treads, one motor driving the treads on one side of a vehicle and the other motor driving the treads on the other side of the vehicle. More particularly, the invention is concerned with an improved mechanical arrangement for controlling the steering and speed functions of the control system.
2. Prior Art
Use of hydraulic cylinders in connection with slot type arrangements to provide the steering functions of hydrostatic control systems is well known but has the disadvantages of being expensive and sometimes troublesome in use. In particular, the cost of manufacturing the slot type arrangement is expensive as are the hydraulic cylinders, the steering valve and required connecting hoses. Further, good steering control through use of hydraulic cylinders is harder to obtain than with a mechanical type arrangement wherein direct control is provided. Also, hydraulic cylinders cause jerk during initial movement from their zero position. Yet further, an all mechanical arrangement is easier to service.
The present invention is concerned with a particularly useful mechanical arrangement which provides control for both the steering and speed functions of a hydrostatic control system. The improved mechanical arrangement of the present invention allows very direct control through its solely mechanical linkage with corresponding direct response of ground engaging means driven by hydrostatic motors the pumps of which are controlled by said linkage. The steering portion of the mechanical arrangement of the present invention is such that it allows spot turns of a vehicle as by rotating one set of wheels or treads on an endless belt in one direction while rotating the wheels or treads on the other side of the vehicle in an opposite direction. These and other advantages realized by the use of the mechanical arrangement of the present invention will become apparent from reading the following description and from examination of the accompanying drawings.